Apparatus for separating solids of relatively different wettabilities



Aug. 1952 E. KLEPETKO ETAL 2,606,660

APPARATUS FOR SEPARATING SOLIDS OF RELATIVELY DIFFERENT WETTABILITIES Filed Sept. 4, 1946 2 SHEETS-SHEET l INVENTORS Ernest Klepnta Lester J l/artzell BY 22AM y ATTORNEYS Aug. 12, 1952 E. KLEPETKO ET AL 2,606,660

APPARATUS FOR SEPARATING souos OF RELATIVELY DIFFERENT WETTABILITIES 2 SHEETS-SHEET 2 Filed Sept. 4, 1946 5 a mu T 6 mm n m By Tim 224M 1m ATTORNEYS Patented Aug. 12, 1952 APPARATUS FOR SEPARATING SOLIDS OF RELATIVELY DIFFERENT WETTABILITIES Ernest Klepetko, Bauer, and Lester J. Hartzell, Jr., Tooele, Utah, assignors to Combined Metals Reduction Company, Stockton, Utah, a corporation of Utah Application September 4, 1946, Serial No. 694,708

3 Claims. 1

This invention relates to cleaning concentrates and the like, and provides an improved method and improved apparatus for producing a clean concentrate from a contaminated starting product. The invention is particularly directed to producing a clean concentrate of particles of a substance that tends to float in an aqueous pulp, from a starting material that in addition contains particles of another substance which is wettable only with some difliculty in the pulp and which therefore tends to float with and contaminate the concentrate. The invention is particularly applicable to producing a clean concentrate composed of particles that are difllcultly wettable from a pulp contaminated with particles of a relatively more wettable, but still rather difficultly wettable, component. In accordance with the invention, provision is made for treating a pulp of the starting product mechanically so as to insure effective wetting of the material which is to be prevented from floating (for example the relatively more wettable component). As a result, this component is caused to sink readily, while the material sought to be recovered in the concentrate (say the diflicultly wettable component) for the most part floats and may be removed separately from the component that has been caused to sink. The invention may be employed with advantage to clean a concentrate previously produced by any suitable method, or it may be used in conjunction with a flotation process making use of a reagent that promotes preferential flotation of one of the components of the starting product.

A number of valuable minerals are diiiicult to wet with water, such, for example, as graphite, molybdenum sulphide, fossil resins, etc. Often an ore or other product containing such a material is beneflciated by a flotation process, in the course of which a pulp of the ore is treated with a reagent capable of causing preferential flotation of the diflicultly wettable material. The floated material then is separated from the pulp as a concentrate. The concentrate usually is contaminated to some extent by other materials present in the ore. Sometimes the contaminants are mechanically bound to the particles of the material sought to be recovered in the concentrate. In such a case the contaminant cannot be separated from the desired material without first breaking this mechanical bond. On the other hand, the contaminant often is present in the concentrate because it, too; floats to some extent in the pulp, and so is withdrawn with the floating material sought to be recovered in the concentrate. This is particularly true if the contaminant is finely divided and does not become wetted very readily by the pulp.

We have discovered that if a pulp of a concentrate or other product containing both a floatable, diflicultly wettable component and a relatively more wettable contaminant is treated so as to force the solid components downwardly into the pulp one or more times after they first begin to rise in the pulp, wetting of the relatively more wettable component is promoted. In consequence sinking of the more wettable component is favored, and a clean floated concentrate of the diflicultly wettable component is produced, relatively free of contamination by particles of the more readily wetted component.

Based on this discovery, the method of our invention involves cleaning a concentrate or other starting product comprising a diflicultly wettable component and a relatively more wettable component by introducing the starting product into an aqueous pool. The particles of both components of the starting product that tend to float to the surface then are mechanically forced downwardly one or more times to well beneath the surface of the pool, whereby the relatively more wettable particles are wetted sufliciently to enable them to sink, and the difiicultly wettable particles are insufficiently wetted to prevent them from floating. The relatively more wettable material may thereafter be withdrawn from beneath the surface of the pool, and the difficultly wettable material may be withdrawn from adja-- cent the surface of the pool.

The new method may be employed in conjunc tion with treating a pulp of the starting material by flotation with a flotation'reagent capable of promoting selective flotation of the desired component. In this case it is not necessary that the component intended to be floated be of. diflicultly wettable character, as the flotation treatment will itself insure that it floats. The method also may be applied to the cleaning of a previously prepared flotation concentrate or similar product containing a floatable difficultly wettable constituent admixed with a relatively more wettable component which, when thoroughly wetted, will sink in a pulp of the product.

We have found that wetting of the material not supposed to be floated is promoted if the starting product is introduced into the pool wherein it is treated at a point below the surface of the pool.

As a part of our invention, we provide apparatus for promoting separation of finely divided difiicultly wettable material from a starting prodnot containing a finely divided relatively more wettable material, in accordance with the method above described, which comprises a vessel for containing a pool of an aqueous pulp of the starting product. The apparatus further comprises means for mechanically forcing particles rising toward the surface of the pulp downwardly one or more times to well beneath the surface of the pulp, thus insuring effective wetting of the relatively more wettable component. A concentrate discharge outlet is provided for withdrawing the diflicultly wettable material from adjacent the surface of the pulp, and means are provided for withdrawing the relatively more wettable material from beneath the surface of the pulp.

In a particularly satisfactory apparatus according to the invention, paddles are mounted adjacent the surface of the pulp in the vessel, and provision is made for actuating the paddles so as to force rising particles of the solid component of the pulp downwardly one or more times to well beneath :the surface of the pulp.

It is advantageous in carrying out the method of our invention to trap the rising solid components of the pulp on a porous screen element and thereby force them downwardly against a wash of the pulp water. In this fashion wetting of the particles not desired to have float is promoted. Accordingly, the apparatus of the invention advantageously comprises paddle wheels or other elements for mechanically forcing the pulp solids downwardly which are made in large part of porous screen mesh material.

The apparatus may be in the form of a cleaner for treating a pulp of concentrates previously produced in any desired fashion, or it may be in the form of a flotation cell modified to carry out the new method in conjunction with a selective flotation operation.

The invention has been employed with marked success in cleaning resin concentrates produced by flotation of fossil resin from resin-bearing coal (although, as indicated above, it may be employed advantageously for producing a clean concentrate of other materials such as graphite, molybdenum sulphide, etc.). Accordingly, an embodiment of the invention as advantageously employed in producing a clean coal-resin concentrate is described below by way of example, with particular reference to the accompanying drawings, in which Fig. 1 is a plan of concentrate cleaning apparatus constructed in accordance with the invention;

Fig. 2 is a section taken substantially along the line 2-2 of Fig. 1;

Fig. 3 is an end view partially in section taken substantially along the line 33 of Fig. 2; and

Fig. 4 is a cross section through an air-lift type of flotation cell as modified to embody features in accordance with the invention.

The apparatus shown in Figs. 1 to 3 comprises a vessel I containing a pool I I of an aqueous pulp in which the solid components comprise particles of the diflicultly wettable material intended to be floated (such as resin particles), and particles of the relatively more wettable component which are to be caused to sink (such as coal particles). The surface I2 of the body of pulp is maintained at a proper level within the vessel by an overflow weir I3, through which excess liquid is discharged. The level of the surface I2 is maintained by the weir IS a very short distance below the upper surface of a concentrate discharge lip I4.

The bottom I5 of the vessel It slopes upwardly from the end containing the concentrate discharge lip I4 to the opposite end, where a collecting box I6 is located for receiving the components of the pulp that have been caused to sink in the vessel. The bottom Id of the vessel also slopes downwardly from each side wall (as best shown in Fig. 3) to a central trough in which a screw conveyor IT is mounted. The screw conveyor is rotated by a belt i3 and motor drive (not shown) in the proper direction to cause material settling to the bottom of the vessel to be conveyed upwardly and out of the vessel into the collecting box I6.

Mounted .over the deep end of the vessel Iii are a series of rotors I9 which extend substantially entirely across the interior width of the vessel. The rotors I9 dip a short distance beneath the normal surface level I2 of the pulp within the vessel. Each rotor carries a series of radial paddles 29. These paddles are made mainly of fine mesh wire screen, with only such solid structural parts as are necessary to support the screen. Provision is made for driving all of the rotors (by belts .2! and pulleys 22 suitably connected to a motor drive-not shown) in a direction such that the paddles 20, when below the surface of the pulp, tend to advance the solid constituents of the pulp toward the concentrate discharge lip It. This direction of rotation is clockwise when the rotors are viewed as in Fig. 2.

Incoming concentrate or other material to be cleaned enters the vessel through a feed pipe 23 advantageously communicating with the vessel at a point below the surface I2 of the pulp, and advantageously positioned between the pair of rotors at the end of the series most remote from the concentrate discharge Id.

The end 24 of the vessel adjacent the collecting box IE maybe built up around the screw conveyor to form a dam for preventing any floating solids that may'reach this end of the vessel from entering the collecting box.

Operation of the above-described apparatus in carrying out the method of the invention is sub stantially as follows:

After the pool I I of pulp has been established within the vessel to the level determined by the overflow weir I3 (which advantageously is very slightly below the upper surface of the concentrate discharge lip l4 and may be below the level of the screw-conveyor discharge into the collecting box IE), the screw conveyor I1 and the rotors 20 are set in motion. Finely divided coal resin concentrate or other product to be cleaned is delivered (advantageously in the form of an aqueous pulp) to the vessel through the feed inlet 23. The difficulty wettable resin particles (or other material to be collected in the floated concentrate) present in the feed, together with some of the more readily wettable but still not completely wetted coal particles (or other contaminant), tend to rise to surface I2 of the pulp. Such tendency to float appears to be due to the presence of small fissures, holes, or other surface irregularities containing minute air pockets. So long as the particle is not efiectively wetted, the air pockets remain and lower the density of the particles as a whole to a sufficiently low value to enable it to float. Where flotation concentrates are being treated a tendency to float may also be due to residual flotation reagent on the particles, so that the particles become attached to and tend to rise with air bubbles introduced into the pulp. Air bubbles may be introduced along with the feed entering through the inlet 23, or may be introduced in consequence of the action of the paddles 20 on the pulp.

Whatever may be the exact reason for the tendency of the solid particles to float, the particles rising in the pulp are trapped by the paddles 2|], and during the downward motion of the paddles are carried to a point well below the surface of the pulp. As the paddles 20 move through the pulp, the water of the pulp flows through the meshes of the screen so that the solid components trapped by the screen are subjected to a wash ofthe pulp water. The effect of the re-submergence of the rising solid particles, aided by the washing effect achieved by the use of screen mesh paddles, is to promote wetting of the particles to the limit of their ability to be wetted. In the case of the diflicultly wettable resin particles, this effect is small or even negligible. In the case of the more readily wettable coal particles, however, the result is to wet them effectively. These latter particles, after becoming effectively wetted, no longer tend to float, and their settlement in the pulp thereby is facilitated. On the other hand, the diflicultly wettable resin particles still tend to rise to the surface.

Each rotor and its attached paddles, in addition to forcing re-submergence of rising solid particles, advances these particles through the pulp toward the next rotor nearer the concentrate discharge. This rotor in turn causes resubmergence of rising solid particles in the pulp, and advances them toward the next rotor, and so on. As the rising particles are repeatedly resubmerged and advanced toward the concentrate discharge, they comprise a continually smaller proportion of the more readily wettable coal particles, because such particles have become wetted and have tended to sink to the bottom of the vessel. The resin concentrate pushed over the discharge lip I 4, by the paddles of the rotor nearest thereto is substantially cleaned in the sense that it consists only of the particles that have persistently tended to rise in the pulp, and it therefore is substantially free of the more readily wettable coal particles.

The particles that have settled to the bottom of the vessel, comprising chiefly coal particles that have been effectively wetted as a result of the repeated re-submergence treatment, settle toward the screw conveyor l5 at the bottom of the vessel. This conveyor moves the settled particles upwardly along the bottom of the vessel and discharges them into the collecting box Hi, from which they are suitably withdrawn.

Delivery of the incoming feed product through the inlet 23 at a point between the pair of rotors most remote from the concentrate discharge, rather than at a point behind the most remote of these rotors, serves to prevent any particles rising from the feed inlet from escapin the pad dles and from being carried back toward the overflow weir I3. The location of the feed inlet 23 at a point below the surface of the pulp, so that the incoming material is immediately submerged therein, contributes materially to wetting of the more readily wettable coal component of the feed, and so enhances the efficiency of the apparatus.

The arrangement of the rotors so that they dip a short distance below the surface of the pulp insures resubmergence of particles rising even in close proximity to the surface of the rotor. Particles rising in thi region, as well as those rising farther out from the surface of the rotor, thus are not merely swept forward by the paddles without being re-submerged.

Although the arrangement of rotors and paddles described above is an advantageous and simple means for forcing re-submergence of the risin particles, the invention is not limited to the use of this particular arrangement. Reciprocating arms or paddles, or any other mechanical means capable of re-submerging the rising particles, may be employed successfully.

Treatment of a resin concentrate obtained by flotation of the resin from resin-bearing coal (as described, for example, in either of the copending application Ernest Klepetko, Lester J. Hartzell, Jr., and Philip deB. Kaye, Serial No. 686,132, filed July 25, 1946, or U. S. Patent No. 2,506,301 of the same inventors) in the manner and apparatus described above, resulted in very effective separation of the difficultly wettable resin from the more readily wettable coal contaminant present in the flotation concentrate. The resin concentrate discharged over the lip 14 was very largely freed from the coal particles that were not effectively wetted during the flotation treatment, and that therefore floated with the resin concentrate. The coal that settled in the apparatus and that was removed by the action of the screw conveyor 11 contained only a small proportion of rather coarse resin particles. It was not evident that these particles had become wetted, but apparentl theywere too large to be floated by whatever air pockets may have been held thereon or therein by surface tension. The coal discharge collected in. the box-l6 was returned to the flotation circuit to recover these resin particles.

The apparatus shown in Figs. 1 to 3 is particularly advantageous for cleaning'a concentrate or other product previously prepareduby selective flotation or by other means. The invention may, however, be employed with success in conjunction with selective flotation treatment of some ores and other raw materials. Fig. 4 shows a fiotation'cell as modified to apply the principles of the present invention to the treatment of an ore pulp (or other pulp) while concurrently subjecting the pulp to, a, flotation operation.

The apparatus shown in Fig. 4 comprises a Forrester type air-lift flotation cell 30 having the usual sloping bottom 3|, sides 32 and ends 33. The cell in operation is filled with a pulp of the ore to be treated, the upper surface of the pulp being but slightly below the upper edge of the concentrate discharge lips 34. Air is introduced into the pulp near the bottom of the cell through air pipes 35 (only one is shown in the drawing), arranged at intervals along the length of the cell and supplied through a header 36. Baffies 37 spaced from the bottom of the cell confine the rising bubbles of air introduced through the pipe 35 and so produce an air lift effect causing circulation of the pulp downwardly between the sloping bottom 3| and baflles 31, and'upwardly through the space between the baffles 31. The aerated pulp overflowing at the top of the baffles 3-1 flows out toward the sides 32 of the cell. Splash boards 38 confine splashing caused by the air lift to the central portion of the cell.

In the normal operation of this type of flotation cell, the reagent-treated ore pulp is introduced into the cell, and the particles which the reagent causes to float overflow with the airbubble froth into concentrate collecting launders 39. The unfioated material is withdrawn through 7 a discharge not-shown) located near the bottom of the cell.

In floating a r'esin concentrate "from coal in a cell of this'c'haracter, an'appre'ciable quantity of coal will float with the resin and be discharged into the concentrate launders 39 because it has not been effectively 'wetted 'in the pulp. In accorda'nce with' the invention, this result is substantially prevented by theprovision of rotors is equipped with paddles 4|. The rotors preferably dip slightly below the surface of the pulp, and are rotated'in a direction 'to'advance the floating concentrate toward the discharge lips '34.

The'resin and other particles floating toward the surface of the pulp are trapped by the paddles on the rotating rotors lll, and are re-submerged one or more times as they areadvanced toward the concentrate overflow. In'consequence of this re-submergenc'e, wetting of the particles not intended to be floatedis promoted. The tendency for these particles to sink in the pulp thus is enhanced, and the concentrate swept over the discharge lips 34 by the paddles on the rotors nearest thereto is substantially free from coal particles that, if not Wetted, would be likely to accompany the resin concentrate.

As in the case of the apparatus described in Figs. 1 to 3, the paddles 4| are advantageously made of fine screen mesh material, so that when the floating particles are re-submerged thereby they are swept against a Wash of the pulp water.

When the invention is employed in conjunction with flotation treatment of an ore pulp, as above described with reference to Fig. 4, it is not necessary that the floating concentrate be non-wettable or diflficultly wettable. In such a case, the flotation reagents and "aeration of "the pulp is generally suihcient to insure flotation of this component of the pulp. But if there are components in the pulp which are not intended to be floated and which do not become wetted promptly after incorporation in the .pulp', or after introduction of the pulp 'into the flotation cell, surface tension "effects may tend to cause floating of thesmall particles of this component. Thus they are likely to be collected with and contaminate the concentrate. The method and apparatus of the invention may be used with advantage in the treatment of such 'pulp's during flotation, as thereby wetting of the particles not supposed to be floatedis promoted, and their'tendency to float with the'concentrate is accordingly-reduced. In such a case, therefore, the method and apparatus of the invention will improve the quality of the concentrate even though the particles intended to be floated are in themselves not diflicult to wet.

Weclaim:

1. Apparatus for promoting separation of finely divided diflicultly wettable material from finely divided relatively more wettable material which comprises a vessel for containing a pulp of said materials, paddles mounted adjacent the surface of the pulp in the vessel, said paddles being made of material which will permit the flow of substantial pulp liquid through them when said paddles are moved through the pulp liquid, means for actuating the paddles to move them into and out of the pulp so as to force particles rising toward the surface of the pulp downwardly against a wash of the pulp liquid one or more times to well beneath the surface of the pulp, a concentrate discharge outlet for withdrawing difficultly wettable material from adjacent the surface of the'pulp, and means for withdrawing the relatively more wettable material from beneath the surface of the pulp.

2. In apparatus of the character described, a vessel adapted to contain a body of pulp, a series of rotors mounted side by side so that their peripheral faces each dip somewhat beneath the normal surface level of the pulp in the vessel, paddles mounted on the rotor faces, said paddles being made of material which will permit the flow of substantial pulp liquid through them when they are moved through the pulp liquid, a concentrate discharge outlet for floating material located adjacent the rotor at one end of the series, and means for rotating the rotors so that the paddle blades force particles of material tending to rise in the pulp downwardly again to well beneath the surface thereof against a wash of pulp liquid, the direction of rotation of the rotors being such as to advance material that persists in floating toward the outlet therefor.

3. In apparatus of the character described, a vessel adapted to contain a body of pulp, a series of rotors mounted side by side so that their peripheral faces each dip somewhat beneath the normal surface level of the pulp in the vessel, paddles made of screen mesh mounted on the rotor faces, said mesh being of such size as to perrnit the flow of substantial pulp liquid through it when moved through the pulp liquid, a concentrate discharge outlet for floating material 10- sated adjacent the rotor at one end of the series, an inlet for introducing fresh pulp into the vessel at a point beneath the surface of the pulp therein and between the two rotors most remote from said outlet, and means for rotating the rotors so that the paddles force particles of material tending to rise in the pulp downwardly again to well beneath the surface thereof against a wash of pulp liquid, the direction of rotation of the rotors being such as to advance material that persists in floating toward the outlet therefor.

ERNEST KLEPETKO. LESTER J. HARTZELL, JR.

REFERENCES mean The following references are of record in the of this patent:

UNITED STATES PATENTS Great Britain Mar. 2, 1938 

